Medium feeding device, recording apparatus

ABSTRACT

A medium feeding device is provided in order to address the problem of double feeding which occur when feeding media to be fed having different hardness. A medium feeding device includes an arm that supports a feeding roller and a placement section wherein a portion of the placement section that opposes the feeding roller is displaceable in directions to come into contact with and be separated from the feeding roller. The medium feeding device is configured such that, when the feeding roller receives a force from the medium as a reaction force against a force acting on the medium by the feeding roller, which causes the arm to move in a direction that causes the feeding roller to move toward the medium, the portion of the placement section is displaced if a pressing force of the feeding roller against the medium exceeds a predetermined amount of force.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese Patent Application No. 2010-057138 filed Mar. 15, 2010, the contents of which are hereby incorporated by reference in their entirety.

BACKGROUND

1. Technical Field

The present invention relates to a medium feeding device including a placement section on which a medium to be fed is placed, feeding means that is in contact with the top medium to be fed of the stack of media stacked in the placement section and feeds the medium to be fed to the downstream region in the feeding direction, and separation means that is provided with an inclined plane which is inclined with respect to the medium to be fed placed in the placement section as seen in a lateral view and separates the top medium to be fed from the subsequent media when the leading edge, i.e., the downstream end of the medium to be fed by the feeding means in the feeding direction, abuts the inclined plane, and a recording apparatus including the medium feeding device. The recording apparatus which is described herein includes ink-jet printers, wire-dot printers, laser printers, line printers, copy machines, facsimile machines and the like.

2. Related Art

JP-A-2001-354330 discloses an image forming apparatus as a recording apparatus that includes a sheet feeding device as a medium feeding device. The sheet feeding device includes a paper feeding tray, a paper feeding roller and a separation slope, and the paper feeding tray is configured so that paper sheets are placed therein. Further, the paper feeding roller is disposed at the distal end of the paper feeding roller arm and is capable of contacting with the top paper sheet of the paper sheets stacked in the paper feeding tray and feeding the paper sheet to the downstream region in the feeding direction. Moreover, the separation slope is disposed downstream in the feeding direction with respect to the leading edge, i.e., the downstream end of the paper sheets stacked in the paper feeding tray and arranged inclined with respect to the leading edge of the stacked paper sheets as seen in a lateral view.

The separation using the above mentioned separation slope, so-called dam separation, utilizes the elasticity, that is, hardness of the paper sheet. This makes it extremely difficult to solve both the problem of double feeding of thin paper sheets and the problem of non-feeding of thick paper sheets at the same time. Accordingly, the separation slope has been configured to be movable in the inclination direction and is biased upstream in the feeding direction by a spring.

When thin paper sheet is used as a paper sheet, since the thin paper sheet has a low paper sheet elasticity, a small transport load is generated when the leading edge of the thin paper sheet moves toward and abuts the separation slope at a first predetermined entering angle. This is because the thin paper sheet easily flexes and the leading edge of the thin paper sheet easily moves up the separation slope. Accordingly, when thin paper sheet is used as a paper sheet, the leading edge of the thin paper sheet can abut the separation slope at the predetermined entering angle and start moving up the separation slope at the entering angle. On the other hand, when thick paper sheet is used as a paper sheet, since the thick paper sheet has a paper sheet elasticity higher than that of the thin paper sheet, a transport load larger than that of the thin paper sheet is generated when the leading edge of the thick paper sheet moves toward and abuts the separation slope at a first predetermined entering angle. This is because the thick paper sheet does not easily flex and the leading edge of the thick paper sheet does not easily move up the separation slope as compared with the thin paper sheet.

Here, the separation slope receives a force from the leading edge of the thick paper sheet. Then, the separation slope moves downstream in the feeding direction against a biasing force of the spring. Here, the position of the leading edge of the thick paper sheet changes, however the contact point between the separation slope and the leading edge remains unchanged. That is, this is the state before the leading edge of the thick paper sheet starts moving up the separation slope. Then, the separation slope further moves downstream in the feeding direction. Here, the entering angle of the leading edge of the thick paper sheet to the separation slope gradually decreases. This results in the transport load gradually decreasing. Accordingly, when thick paper sheet is used as a paper sheet, the leading edge of the thick paper sheet can start moving up the separation slope when the decreased entering angle becomes a second predetermined angle.

However, when thick paper sheet is used as a paper sheet, the above configuration merely decreases the entering angle, thereby decreasing the transport load as compared with the case when thin paper sheet is used. Therefore, it is not enough to overcome the problem of non-feeding of thick paper sheets.

SUMMARY

An advantage of some aspects of the invention is that a medium feeding device that overcomes the problem of double feeding and the problem of non-feeding in the case when media to be fed having different hardness are used, and a recording apparatus including the medium feeding devices are provided.

According to an aspect of the invention, a medium feeding device in a first example is a medium feeding device that feeds a medium placed in a placement section from the placement section to a downstream region in a feeding direction including feeding means that feeds the medium to the downstream region in the feeding direction, the feeding means having a feeding roller that is in contact with the top medium of the stack of media stacked in the placement section, and an arm that is mounted to be movable about a point located above the feeding roller in the stack direction and provided with the feeding roller for rotation at the free end of the arm, and separation means that is provided with an inclined plane so that the leading edge of the medium placed in the placement section abuts the inclined plane and separates the top medium from the subsequent media, wherein a portion of the placement section which opposes the feeding roller is displaceable in directions that allow the portion of the placement section to come into contact with and be separated from the feeding roller, and the feeding roller receives a force from the medium, which causes the arm to move in a direction that causes the feeding roller to move toward the medium, thereby increasing a pressing force of the feeding roller against the medium, such that the portion of the placement section is displaced when the pressing force of the feeding roller against the medium exceeds a predetermined amount of force.

The “predetermined amount of force” is defined as follows. When a medium having a relatively low hardness is used, the amount of the pressing force does not exceed the “predetermined amount of force”, while a medium having a relatively high hardness is used, the amount of the pressing force exceeds the “predetermined amount of force.” That is, when a medium having a hardness higher than a predetermined value is used, a reaction force significantly acts to allow the pressing force to be larger than the “predetermined amount of force”, thereby enabling the medium to move up the inclined plane.

In the first example of the invention, a portion of the placement section can be displaced depending on a hardness of the medium. For example, when a medium has a relatively low hardness, the pressing force of the feeding roller against the medium is below the predetermined amount of force. As a result, the portion of the placement section is not displaced. Accordingly, the entering angle of the medium entering the inclined plane of the separation means remains unchanged. Further, the relative position and posture of the arm and the portion of the placement section are not displaced, therefore a normal force generated between the feeding roller and the medium to be fed remains unchanged. Therefore, a feeding force that feeds the medium in the feeding direction by the feeding roller also remains unchanged. Consequently, the medium having a low hardness can be fed with certainty.

On the other hand, when a medium has a relatively high hardness, when the downstream end of the medium abuts the inclined plane of the separation means, the reaction force acts to a greater extent compared with the case of the medium having a low hardness. Accordingly, a force that acts on the arm to cause the leading edge of the arm to move for engaging with the top medium also increases. Then, the pressing force of the feeding roller against the medium exceeds a predetermined amount of force. As a result, at least a portion of the placement section can be displaced by the pressing force. Here, the position where the downstream end of the medium to be fed abuts the inclined plane of the separation means is not displaced.

That is, while the position of the downstream end of the medium remains unchanged, the upstream area relative to the downstream area of the medium can be displaced. Accordingly, the entering angle of the medium entering the inclined plane of the separation means can be reduced. Therefore, as a first advantageous effect, it is possible to decrease the transport load that is necessary for the leading edge of the medium passing through the separation means. Further, it is possible to increase the normal force, which is generated between the feeding roller and the medium when the arm moves toward the medium. Therefore, as a second advantageous effect, it is possible to increase the feeding force that feeds the medium to be fed in the feeding direction by the feeding roller. Consequently, due to the first and second advantageous effects, the medium having a high hardness as well as the medium having a low hardness can be fed with certainty.

Further, the position of the portion of the placement section is configured so as to allow the medium having a relatively low hardness to be separated by the separation means in the state before the pressing force of the feeding roller against the medium becomes the predetermined amount of the force. Alternatively, the placement section may be configured to elastically deform, thereby allowing the portion of the placement section to be displaced. That is, the portion of the placement section may not necessarily be formed as a separate part from the remaining portion of the placement section, and may be formed integrally with the remaining portion of the placement section. For example, the portion and the remaining portion of the placement section may be formed to be connected by a connection point and allows the portion to be displaced by an elastic deformation of the connection point.

According to a second example of the invention in the medium feeding device of the first example, the medium feeding device can be configured to feed a first medium and a second medium having a hardness higher than that of the first medium, wherein the portion of the placement section is not displaced by the pressing force when feeding the first medium, and the portion of the placement section is displaced by the pressing force when feeding the second medium. Accordingly, in the second example of the invention, the medium feeding device can accommodate to the media having different hardness, in addition to the advantageous effect of the first example.

According to a third example of the invention in the medium feeding device of the first example, the medium feeding device can include bias means that biases the portion of the placement section in a direction so as to move the portion of the placement section toward the feeding roller. Accordingly, in the third example of the invention, the amount of the biasing force can be more accurately determined as compared with the configuration in which the connection point elastically deforms, in addition to the advantageous effect of the first example. That is, the position and posture of the portion of the placement section can be accurately controlled.

As a result, the feeding force can be more accurately controlled. Further, the transport load also can be more accurately controlled. Moreover, the position and posture of the portion of the placement section can be determined at the side close to the feeding roller within the range that the portion of the placement section is displaced by balancing the weight of the medium and the biasing force of the bias means.

According to a fourth example of the invention in the medium feeding device of the third example, the medium feeding device further includes a regulation member that regulates the position at the side close to the feeding roller within the range through which the portion of the placement section is displaced. According to the fourth example of the invention, in addition to the advantageous effect of the third example, the entering angle can be constant, since the position of the placement section is not displaced in the case when the medium having a low hardness is used.

That is, the position as a reference of the portion of the placement section can be determined by the regulation member. Further, in this example, the weight of the medium and the biasing force of the bias means that biases the placement section do not need to be balanced. That is, the regulation member enables the amount of biasing force to be set with greater degree of freedom and facilitates the setting of the biasing force. Consequently, it is possible to easily accommodate to the media having significantly different hardness.

According to a fifth example of the invention in the medium feeding device of the first example, the portion of the placement section is configured to be movable about a position in the downstream area in the feeding direction in the medium feeding device of the first example. According to the fifth example of the invention, in addition to the advantageous effect of the first example, it is possible to actively decrease the entering angle when the portion of the placement section is displaced. Meanwhile, the relative change of the posture of the arm and the portion of the placement section increases during the movement of the arm for allowing the leading edge to engage with the top medium, thereby actively increasing the pressing force. As a result, it is possible to actively increase the transport load and increase the feeding force.

According to a sixth example of the invention in the medium feeding device of the first example, the portion of the placement section is configured to be displaced while maintaining its posture in the medium feeding device of the first example. According to the sixth example of the invention, in addition to the advantageous effect of the first example, the setting of the biasing force is easier as compared with the fifth example in which the portion of the placement section is configured to be movable about a position in the downstream area in the feeding direction. Further, the change of the entering angle and the relative change of the position can be more gradually as compared with the case in which the portion of the placement section is configured to be movable about a position in the downstream area. Therefore, it is possible to prevent the double feeding caused by the abruptly decreased transport load and abruptly increased feeding force.

According to a seventh example of the invention in the medium feeding device of the first example, the placement section is configured such that a portion of the placement section at the downstream area in the feeding direction which opposes the feeding roller is displaceable and an area upstream in the feeding direction relative to the downstream area in the feeding direction is not displaceable in the medium feeding device of the first example. According to the seventh example of the invention, in addition to the advantageous effect of the first example, it is possible to accommodate to the media having different sizes. This is highly effective in that the influence of the weight of all the media to the biasing force that biases the portion of the placement can be reduced.

According to another aspect of the invention, a recording apparatus according to an eighth example of the invention includes the medium feeding device according to the first example and a recording unit that performs recording on the medium which has been fed by the medium feeding device. According to the eighth example of the invention, the recording apparatus can be provided which can achieve the same advantageous effect as that of the first example.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.

FIG. 1 is a side view of a printer according to the present invention.

FIG. 2 is an enlarged side view which schematically shows an essential part of medium feeding means before feeding according to the present invention.

FIGS. 3A and 3B are schematic side views of the medium feeding means during feeding of thin paper sheets.

FIGS. 4A and 4B are schematic side views of the medium feeding means during feeding of thick paper sheets.

FIGS. 5A and 5B are schematic side views of medium feeding means according to alternative embodiment 1.

FIGS. 6A and 6B are schematic side views of medium feeding means according to alternative embodiment 2.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the present invention will be described below with reference to the attached drawings. FIG. 1 is a schematic side view of a printer as an example of recording apparatus according to the invention. As shown in FIG. 1, a printer 1 according to the invention includes medium feeding means 2, a feeding path, a recording unit 16 and discharge unit 20.

The medium feeding means 2 is arranged so that a paper sheet P as an example of medium to be fed is fed in the feeding direction Y. The feeding path is a path along which the paper sheet P is fed and is composed of a medium guiding section that guides the paper sheet P fed by the medium feeding means and the like. The recording unit 16 is configured to perform recording on the paper sheet P which has been fed by the medium feeding means 2. Further, the discharge unit 20 is configured to cause the recorded paper sheet P to be discharged and placed on the discharge tray (not shown).

Specifically, the medium feeding means 2 includes a placement section 6, a pick-up roller 3, an arm 4, separation means 12, a first pair of rollers 14 and a second pair of rollers 15. The placement section 6 is arranged so that paper sheets P are placed therein. The pick-up roller 3 can be actuated by a driving force from a motor and is configured to be in contact with the top paper sheet P of a stack of paper sheets P stacked in the placement section 6.

The arm 4 is arranged to be pivotally movable about a pivot shaft 5 disposed at one end thereof upstream in the feeding direction. Further, the arm 4 supports the pick-up roller 3 for rotation at the other end thereof downstream in the feeding direction. The motor can be disposed in the main body of the printer 1 away from the arm 4, or alternatively, can be disposed on the arm. In the former case, the driving force from the motor is transmitted to the pick-up roller 3 by means of driving force transmission means such as a gear array through the pivot shaft 5. In the latter case, the driving force from the motor is transmitted to the pick-up roller 3 by means of driving force transmission means such as a gear array without passing through the pivot shaft 5.

The separation means 12 is arranged downstream in the feeding direction of the placement section 6 where the paper sheets P are placed. Specifically, the separation means 12 has an inclined plane 13 which is inclined with respect to the paper sheet P to be fed by the pick-up roller 3 as seen in a lateral view. When the paper sheets P are double fed, the separation means 12 operates to separate the top paper sheet P from the subsequent paper sheets P with respect to the pick-up roller 3. This is a so-called dam separation mechanism, which refers to a mechanism that causes the paper sheet P to enter the plane surface at a predetermined angle, thereby applying a load to the leading edge of the paper sheet P in order to achieve the separation.

The first pair of rollers 14 and the second pair of rollers 15 are arranged so as to feed the paper sheet P which has been passed through the separation means 12 to the recording unit 16. The first pair of rollers 14 is composed of a first drive roller 14 a and a first driven roller 14 b. Alternatively, the first driven roller 14 b may be a so-called retard roller, which rotates under a predetermined load. The retard roller can ensure the separation of the double fed paper sheets P if the dam separation mechanism is not enough to separate the double fed paper sheets P. That is, it is possible to separate a paper sheet which is directly in contact with the first drive roller 14 a from the other paper sheets located closer to the retard roller.

The second pair of rollers 15 is arranged downstream of the first pair of rollers 14 in the feeding path. Specifically, the second pair of rollers 15 is composed of a second drive roller 15 a and a second driven roller 15 b and is configured to feed the paper sheet P to the recording unit 16 with a high accuracy by means of, for example, a stepping motor. As a matter of course, when the leading edge of the paper sheet P reaches the second pair of rollers 15, so-called skew removal is performed, correcting the posture of the paper sheet P with respect to the feeding direction Y.

The recording unit 16 includes a carriage 17, a recording head 18 and a medium support unit 19. The carriage 17 is arranged so as to move in the width direction X by means of driving force from moving means (not shown) while being guided along a guide shaft (not shown) which extends in the width direction X of the paper sheet P. The recording head 18 is mounted on the carriage 17 so as to eject ink onto the paper sheet P in order to perform so-called ink jet recording.

Further, the medium support unit 19 is arranged so as to oppose the recording head 18 and is configured to support the paper sheet P and cause the distance between the paper sheet P and the recording head 18 to be a predetermined distance. Although the recording unit 16 in this embodiment is of an ink jet type that ejects ink, other types of recording unit may be used. For example, a so-called laser printer may be used, in which recording is performed by causing toner to adhere to the paper sheet P with heat and pressure.

The discharge unit 20 includes a third pair of rollers 21 and a discharge tray, which is not shown. The third pair of rollers 21 is arranged downstream of the recording unit 16 along the feeding path and is configured to feed the recorded paper sheet P to the discharge tray. The placement section 6 of the medium feeding means 2 may be of a so-called cassette type that is detachaby mounted into the main body of the printer, or alternatively, may be formed integrally with the main body of the printer. The following explains the medium feeding means 2 in detail, which is an essential part of the invention.

FIG. 2 is an enlarged side view which schematically shows an essential part of medium feeding means before feeding according to the invention. As shown in FIG. 2, the placement section 6 is composed of a first placement surface 7 which is located downstream in the feeding direction and a second placement surface 8 which is located upstream of the first placement surface 7. The first placement surface 7 is disposed at a position opposing the pick-up roller 3. Further, the first placement surface 7 is arranged to be displaceable in the direction that causes the first placement surface 7 to come into contact with and be separated from the pick-up roller 3. In this embodiment, the first placement surface 7 is disposed to be displaceable in the stack direction Z of the paper sheets P. On the other hand, the second placement surface 8 is arranged so as not to be displaced, that is, in a fixed configuration.

Further, the first placement surface 7 is biased upward in the stack direction toward the pick-up roller 3 by biasing force from a spring 10 as an example of bias means 9. A regulation member 11 is arranged to determine the position and posture of the first placement surface 7 at the side close to the pick-up roller 3 within the displaceable range. When the first placement surface 7 is in contact with the regulation member 11, the first placement surface 7 comes to be flush with the second placement surface 8, that is, at the same position in the stack direction Z.

Moreover, the regulation member 11 is arranged so as not to obstruct the feeding of the paper sheet P. For example, the first placement surface 7 is formed to be larger in the width direction X than the area in which the paper sheets P are placed. The regulation members 11 can be disposed at both the sides of the first placement surface 7 in the width direction X such that the regulation members 11 are disposed outside the paper sheet P in the width direction X so as not to be in contact with the paper sheets P.

Further, the pick-up roller 3 can be configured to press against the top paper sheet P. For example, a configuration may be used in which the top paper sheet P is pressed by the weight of the pick-up roller 3 and an arm 4. Alternatively, a configuration may be used in which the top paper sheet P is pressed by biasing force from bias means, which is not shown. A spring may be used as the bias means. Further, a configuration may also be used in which kinetic friction between two relatively rotating members generates a force that moves the arm 4 in the direction that causes the pick-up roller 3 to move toward the paper sheet P. This is a configuration that uses a so-called torque limiter in the pivot shaft 5.

In this embodiment, the first placement surface 7 is not displaced in a normal state, in which the first placement surface 7 and the second placement surface 8 are flush with each other. The first placement surface 7 is arranged so as not to be displaced before feeding of the paper sheet P. Specifically, in this configuration, the following relationship is established: pressing force N+weight W of the paper sheet<spring force S, where N is a pressing force that presses the paper sheet P exerted by the pick-up roller 3, W is the weight of the paper sheet P that acts on the first placement surface 7 and S is a force of the spring 10 when the first placement surface 7 is in the non-displaced position.

Although the regulation member 11 is provided in this embodiment, it may not necessarily be provided. For example, if the relationship pressing force N+weight W of the paper sheet=spring force S is established when the first placement surface 7 is in the non-displaced position, the relationship of the forces are balanced, and therefore the first placement surface 7 can be stable at the non-displaced position. In this case, the regulation member 11 may be omitted. The regulation member 11 is provided in this embodiment, because this enables the amount of force applied by the spring 10 to be set with a greater degree of freedom, and further, the first placement surface 7 to be more highly stabilized in the non-displaced position.

Feeding of Thin Paper Sheets (First Media)

FIGS. 3A and 3B are schematic side views of the medium feeding means during feeding of thin paper sheets. FIG. 3A shows the state in which the leading edge of the thin paper sheet abuts the surface of the inclined plane, while FIG. 3B shows the state in which the thin paper sheet is further advanced after the state shown in FIG. 3A. The term “thin paper sheet” as used herein refers to a paper sheet having a relatively small thickness and a relatively low elasticity. The term “thin paper sheet” more specifically refers to a concept of a “first medium” which is a medium having a relatively low elasticity.

As shown in FIG. 3A, as the pick-up roller 3 rotates in a clockwise direction as viewed in the figure, the top sheet P1 of the thin paper sheets can be fed to a downstream region in the feeding direction. A transport load R is a load for feeding the paper sheet P to the downstream region in the feeding direction and a feeding force F is a force that is exerted on the paper sheet P by the pick-up roller 3. The feeding force F is obtained from a friction coefficient μ between the pick-up roller 3 and the paper sheet P and the pressing force N of the pick-up roller 3 that presses the paper sheet P.

The frictional force acting between the top sheet of paper sheets and the subsequent paper sheets is small before the leading edge of the paper sheet P abuts the inclined plane 13 of the separation means 12. In other words, the frictional force is significantly smaller than the load generated when the leading edge of the paper sheet P abuts the inclined plane 13 of the separation means 12, as described later. Accordingly, the transport load R is small before the leading edge of the paper sheet P abuts the inclined plane 13. The thin paper sheet P1 is moved toward and abuts the inclined plane 13 at an entering angle θ1.

Upon abutting, the transport load R increases. Here, the friction coefficient μ and the inclined plane 13 and the like are configured such that the following relationship is established for the top sheet of the thin paper sheets P1:

transport load R<feeding force F

On the other hand, the following relationship is established for the subsequent thin paper sheets P1:

transport load R>feeding force F

Therefore, even if the subsequent thin paper sheets P1 are dragged by the top sheet P1 of the thin paper sheets and fed to a downstream region in the feeding direction, the leading edges of the subsequent thin paper sheets P1 can be stopped by the inclined plane 13. That is, the subsequent thin paper sheets P can be separated from the top sheet P1 of the thin paper sheets.

As the transport load R increases when the leading edge of the thin paper sheet P1 abuts the inclined plane 13, a significant force is generated toward the upstream region in the feeding direction as a reaction force that acts on the pick-up roller 3. The arm 4 is arranged to pivotally move about a point which is located upstream of the pick-up roller 3 and above the top sheet P1 of the thin paper sheets in the stack direction. Therefore, a force acts so as to pivotally move the arm 4 in the direction that causes the downstream end, i.e., a free end of the arm 4 where the pick-up roller 3 is mounted to move toward the thin paper sheets P1.

However, in the case when the thin paper sheet P1 having a low paper sheet elasticity is used, the force to pivotally move the arm 4 is smaller than that in the case when the second medium is used as described later. The force to pivotally move the arm 4 causes the pressing force of the pick-up roller 3 acting on the thin paper sheet P1 to increase. In the case when the first medium (P1) is used, the increased amount of the pressing force does not exceed a predetermined amount of the force (the amount of the spring force S of the spring 10 minus the weight W of the paper sheet). Therefore, the following relationship can be maintained:

the increased pressing force N+weight W of the paper sheet≦spring force S

Therefore, in the case when the thin paper sheet P1 (first medium) is used, the first placement surface 7 is not displaced.

As shown in FIG. 3B, since the thin paper sheet P1 has a low paper sheet elasticity, the thin paper sheet P1 moves up the inclined plane 13 with the leading edge being flexed. That is, the thin paper sheet P1 can be separated from the subsequent sheets with the entering angle θ1 with respect to the inclined plane 13. The thin paper sheet P1 can be further advanced downstream in the feeding direction, since the following relationship is established:

transport load R<feeding force F

Feeding of Thick Paper Sheets (Second Media)

FIGS. 4A and 4B are schematic side views of the medium feeding means during feeding of thick paper sheets. FIG. 4A shows the state in which the leading edge of the thick paper sheet abuts the surface of the inclined plane, while FIG. 4B shows the state in which the pick-up roller is slightly actuated after the state shown in FIG. 4A. The term “thick paper sheet” as used herein refers to a paper sheet having a relatively larger thickness than that of the thin paper sheet and a relatively higher elasticity than that of the thin paper sheet. The term “thick paper sheet” more generally refers to a concept of a “second medium” which is a medium having a relatively higher elasticity than that of the “first medium”.

As shown in FIG. 4A, as the pick-up roller 3 rotates in a clockwise direction as viewed in the figure, the top sheet P2 of the thick paper sheets can be fed to a downstream region in the feeding direction. Then, the leading edge of the thick paper sheet P2 can abut the inclined plane 13 in a similar manner as the thin paper sheet P1. The thick paper sheet P2 abuts the inclined plane 13 at an entering angle θ1, which is the same as that of the thin paper sheet P1. The thick paper sheet P2 differs from the above mentioned thin paper sheet P1 in that it has a higher paper sheet elasticity than that of the thin paper sheet P1.

Therefore, when the leading edge of the thick paper sheet P2 abuts the inclined plane 13, the transport load R increases to a greater extent than that of the case when thin paper sheet P1 is used. This is because the thick paper sheet P2 requires a greater amount of force to flex than the thin paper sheet P1 does, since the thick paper sheet P2 has a higher elasticity than that of the thin paper sheet P1. In other words, after the thick paper sheet P2 abuts the inclined plane 13, the feeding force increases until the thick paper sheet P2 flexes. The feeding force increases to a greater extent than that of the case when the thin paper sheet P1 is used. That is, the thick paper sheet P2 requires a greater amount of feeding force than the thin paper sheet P1 does.

Then, a significant force is generated toward the upstream in the feeding direction as a reaction force that acts on the pick-up roller 3. The amount of the reaction force is significantly larger than that of the thin paper sheet P1. Therefore, a force acts to pivotally move the arm 4 in the direction that causes the downstream end, i.e., a free end of the arm 4 where the pick-up roller 3 is mounted to move toward the thick paper sheet P2. The amount of the force is significantly larger than that of the case when the thin paper sheet P1 is used. That is, the reaction force that acts on the arm 4 to allow the pick-up roller 3 mounted at the free end of the arm 4 to engage with the thick paper sheet P2 is significantly larger than that of the case when the thin paper sheet P1 is used. Therefore, the increase of the force pressing the thick paper sheet P2 by the pick-up roller 3 is also significantly larger than that of the case when the thin paper sheet P1 is used.

Accordingly, in the case when the second medium (P2) is used, the increased amount of the pressing force is larger than a predetermined amount of the force (the amount of the spring force S of the spring 10 minus the weight W of the paper sheet). Therefore, the following relationship can be established:

the increased pressing force N+weight W of the paper sheet>spring force S

As shown in FIG. 4B, the first placement surface 7 is pressed down, reacting against the spring force S of the spring 10. Here, the leading edge of the thick paper sheet P2 is in contact with the inclined plane 13 with the contact point between the thick paper sheet P2 and the inclined plane 13 being not displaced. As a result, the thick paper sheet P2 flexes at the proximity of the leading edge, therefore the entering angle θ1 of the thick paper sheet P2 with respect to the inclined plane 13 decreases to θ2. As a result, the first advantageous effect is achieved in which the transport load R in the non-displaced state to decrease to R′. That is, the decreased entering angle can facilitate the leading edge of the thick paper sheet P2 to move up the inclined plane 13, thereby decreasing the transport load.

Further, when the first placement surface 7 is displaced, the arm 4 is inclined to a greater extent with respect to the feeding direction Y of the paper sheet at the position where the pick-up roller 3 is in contact with the thick paper sheet P2. As a result, a force that acts on the arm 4 so that the pick-up roller 3 exerts the engaging force, that is, the engaging force of the arm 4 significantly increases. Therefore, this allows the above mentioned increased pressing force N that presses the paper sheet P by the pick-up roller 3 in the non-displaced state to increase to N′, which is significantly greater than N.

The “engaging force” is described below assuming that the arm inclines at different angles and exerts the same amount of pressing force N when the pick-up roller is not actuated. In this case, once the pick-up roller is actuated, the greater the inclination of the arm 4 with respect to the feeding direction Y of the paper sheet toward the perpendicular position, the greater feeding force F is applied at the position where the pick-up roller 3 is in contact with the thick paper sheet P2. This is because the arm 4 acts as a so-called wedge. As a result, the second advantageous effect is achieved in which the feeding force F that acts on the thick paper sheet P2 by the pick-up roller 3 in the non-displaced state increases to F′, which is significantly greater than F. That is, the significantly increased feeding force can facilitate the leading edge of the thick paper sheet P2 to move up the inclined plane 13.

Moreover, since the amount of elastic deformation increases, the spring force S of the spring 10 in the non-displaced state increases to S′. In the displaced state, the following relationship is established:

the increased pressing force N′+weight W of the paper sheet≧spring force S′

In addition, when the first placement surface 7 is in the displaced state, the first placement surface 7 may not necessarily be positioned at the lowest position in the stack direction within the displaceable range. If the first placement surface 7 is displaced to the lowest position, the following relationship is established:

the increased pressing force N′+weight W of the paper sheet>spring force S′

On the other hand, if the first placement surface 7 is not displaced to the lowest position, forces are balanced, therefore the following relationship is established:

the increased pressing force N′+weight W of the paper sheet=spring force S′

As described above, since the first placement surface 7 is configured to be displaced, the top sheet P of the paper sheets can be fed to the recording unit 16 via the separation means 12 in both cases when the thin paper sheet P1 (first medium) is used and the thick paper sheet P2 (second medium) is used as the paper sheet. That is, it is possible to eliminate a so-called non-feeding problem, in which the top sheet P of the paper sheets of either the thin paper sheet P1 (first medium) or the thick paper sheet P2 (second medium) cannot pass through separation means 12. Further, the inclined plane 13 of the separation means 12 does not need to be a complex configuration.

In the above described embodiment, the placement section 6 is composed of the first placement surface 7, which is displaceable, and the second placement surface 8, which is not displaceable. This is because, when the different sizes of the paper sheets are used, the influence to the displacement of the first placement surface 7 caused by the difference of the weight W of the paper sheets can be reduced. Although the first placement surface 7 extends over both sides of the paper sheet P in the width direction X, it is not limited to this configuration. The first placement surface 7 may be formed so as to oppose at least the pick-up roller 3 in the width direction X, because the inclined plane 13 is disposed in the area that opposes the pick-up roller 3.

In addition, although the first placement surface 7 and the second placement surface 8 are separately formed, they may be formed integrally with each other. In this case, the connection point between the first placement surface 7 and the second placement surface 8 can be configured to elastically deform, thereby allowing the first placement surface 7 to be displaced. Further, the spring 10 is used as an example of bias means 9 that changes the amount of biasing force in response to the amount of elastic deformation. However, in the technical concept of this invention, the bias means 9 may not necessarily change the amount of biasing force as long as it can apply a biasing force. For example, a biasing force by blowing an air may be used. In the configuration in which a biasing force does not change, this allows the first placement surface 7 to be easily displaced.

Further, the above described embodiment is described using two types of paper sheets, that is, the thin paper sheet P1 and the thick paper sheet P2, having different hardness. However, the paper sheets are not limited to the two types. In the technical concept of this invention, the first placement surface 7 may be configured so that the amount of displacement can vary depending on the hardness of the paper sheet, thereby accommodating to the three or more types of paper sheets having different hardness. Specifically, if a medium has an elasticity that is higher than that of the thick paper sheet P2, the first placement surface 7 may be displaced to greater extent than that of the case when the thick paper sheet P2 is used. That is, the first placement surface 7 can accommodate to the media having different hardness by increasing the amount of displacement depending on the hardness of each medium. The first placement surface 7 can be configured not to be displaced for the medium that has the lowest hardness and displaced for the medium that has the second lowest hardness.

The medium feeding means 2 as an example of medium feeding device according to an embodiment of the invention includes the placement section 6 on which the paper sheets P as an example of media to be fed are placed, the feeding means that is in contact with the top paper sheet P of the stack of the paper sheets P stacked in the placement section 6 and feeds the paper sheet P to the downstream region in the feeding direction, and the separation means 12 that is provided with an inclined plane 13 which is inclined with respect to the paper sheet P placed in the placement section 6 as seen in a lateral view and separates the top paper sheet from the subsequent paper sheets with respect to the feeding means when the leading edge, i.e., the downstream end of the paper sheet P to be fed by the feeding means in the feeding direction abuts the inclined plane 13, wherein the feeding means has the pick-up roller 3 as a feeding roller that is configured to be actuated and come into contact with the paper sheet P placed in the placement section, and an arm 4 that is pivotally movable about a pivot shaft 5 located upstream of the pick-up roller 3 in the feeding direction Y and above the pick-up roller 3 in the stack direction Z and provided with the feeding roller for rotation at the free end of the arm, and the first placement surface 7 as a portion of the placement section 6 which at least opposes the pick-up roller 3 is displaceable in directions that allow the first placement surface 7 to come into contact with and be separated from the pick-up roller 3, and the pick-up roller 3 receives a force from the paper sheet P as a reaction force against a feeding force F acting on the paper sheet P by the actuating pick-up roller 3, which causes the arm 4 to move in a direction that causes the pick-up roller 3 to move toward the paper sheet P, such that the first placement surface 7 of the placement section 6 is displaced downward in the stack direction when a pressing force N (N′) as a force of the pick-up roller 3 that presses against the paper sheet P exceeds a predetermined amount of force (the spring force S−the weight W of the paper sheets).

Further, the medium feeding means 2 according to an embodiment of the invention is configured to feed the thin paper sheet P1 as an example of a first medium to be fed and the thick paper sheet P2 as an example of a second medium to be fed having a hardness higher than that of the thin paper sheet P1, and wherein the first placement surface 7 of the placement section 6 is not displaced by the pressing force N when feeding the thin paper sheet P1, and the first placement surface 7 of the placement section 6 is displaced by the increased pressing force N (N′) when feeding the thick paper sheet P2.

Further, the medium feeding means 2 according to an embodiment of the invention further includes the bias means 9 that biases the first placement surface 7 of the placement section 6 in the direction to move toward the pick-up roller 3. Further, the medium feeding means 2 according to a forth embodiment of the invention further includes the regulation member 11 that regulates the position at the side close to the pick-up roller 3 within the range that the first placement surface 7 of the placement section 6 is displaced.

Further, the medium feeding means 2 according to an embodiment of the invention, the first placement surface 7 of the placement section 6 is configured to be displaced maintaining its posture. Further, the medium feeding means 2 according to an embodiment of the invention, the placement section 6 is configured such that the first placement surface 7 of the placement section 6 at the downstream area in the feeding direction Y which opposes the pick-up roller 3 is displaceable and the second placement surface 8 which is located upstream in the feeding direction relative to the first placement surface 7 of the placement section 6 is not displaceable. The printer 1 as an example of recording apparatus according to an embodiment of the invention includes the medium feeding means 2 that feeds the paper sheet P as an example of medium to be recorded in the feeding direction Y and the recording unit 16 that performs recording on the paper sheet P which has been fed by the medium feeding means 2 using the recording head 18.

Alternative Embodiment 1

FIGS. 5A and 5B are schematic side views of medium feeding means according to alternative embodiment 1. FIG. 5A shows the state in which the first placement surface is not displaced, while FIG. 5B shows the state in which the first placement surface is displaced. As shown in FIGS. 5A and 5B, a first placement surface 31 of medium feeding means 30 according to the alternative embodiment 1 is formed so that the upstream area to be pivotally movable about the support shaft 32 which is located at the downstream area in the feeding direction. The other components are the same as those described in the abovementioned embodiment, therefore designated by the same references and will not be described further.

Since the first placement surface 31 is configured to pivotally move about the support shaft 32, it is possible to more actively decrease the entering angle θ2 when the first placement surface 31 is displaced in the case when the thick paper sheet P2 is used, compared with the abovementioned embodiment. That is, even when the displacement amount of the upstream area of the first placement surface 31 is the same as that of the abovementioned embodiment, the entering angle θ2 can be smaller than that in the abovementioned embodiment. Consequently, it is possible to more actively decrease the transport load R′ which is the first advantageous effect of the invention, compared with the abovementioned embodiment.

Further, the leading edge of the thick paper sheet P2 can be inclined with respect to the inclined plane 13, so as to release the leading edge of the thick paper sheet P2 to allow the leading edge of the thick paper sheet P2 to move up the inclined plane 13. This can facilitate the leading edge of the thick paper sheet P2 to move up inclined plane 13. Meanwhile, the relative change of the position of the arm 4 and the first placement surface 31 increases during the movement of the arm 4 for allowing the leading edge to engage with the top sheet of the thick paper sheets P2, thereby actively increasing the engaging force. Consequently, it is possible to more actively increase the feeding force F′ which is the second advantageous effect of the invention, compared with the abovementioned embodiment. In the case when the thin paper sheet P1 is used, the first placement surface 31 is not displaced as described in the abovementioned embodiment when the thin paper sheet P1 is used, therefore will not be described further.

In the alternative embodiment 1, the first placement surface 31 of the placement section 6 is configured to pivotally movable about the support shaft 32 which is located at the downstream area in the feeding direction.

Alternative Embodiment 2

FIGS. 6A and 6B are schematic side views of medium feeding means according to alternative embodiment 2. FIG. 6A shows the state in which the first placement surface is not displaced, while FIG. 6B shows the state in which the first placement surface is displaced. As shown in FIGS. 6A and 6B, medium feeding means 40 according to the alternative embodiment 2 has a placement surface 41. The other components are the same as those described in the abovementioned embodiment, therefore designated by the same references and will not be described further.

The placement surface 41 is configured to be displaceable in a similar manner as the first placement surface 7 does as described in the abovementioned embodiment. In other words, the placement surface 41 corresponds to the configuration in which the first placement surface 7 and the second placement surface 8 (see FIGS. 2 to 4) are integrally formed so that the second placement surface 8 is displaced along with the first placement surface 7. Therefore, when the placement surface 41 is displaced in using the thick paper sheet P2, the entering angle θ1 can be decreased to θ2 in a similar manner as the abovementioned embodiment.

Meanwhile, the arm 4 moves for allowing the leading edge to engage with the top sheet of the thick paper sheets P2. This enables the feeding force F to increase to F′ in a similar manner as the abovementioned embodiment. In the case the thin paper sheet P1 is used, the placement surface 41 is not displaced as described in the above-mentioned embodiment when the thin paper sheet P1 is used, therefore will not be described further. As a matter of course, in the non-displaced state, the position and posture of the placement surface 41 are determined by the regulation member (see FIG. 2).

Alternative Embodiment 3

In the embodiments described above, the pick-up roller 3 moves toward the paper sheets P placed in the placement section 6 in order to feed the paper sheet P. That is, as the number of the paper sheets P left in the placement section 6 decreases, the pick-up roller 3 moves downward. In alternative embodiment 3, the placement section is movable toward and away from the pick-up roller. In this configuration, regardless of the number of the paper sheets P left in the placement section, the difference in position of the arm 4 can be reduced. Therefore, it is possible to reduce the change of the pressing force N of the pick-up roller to press the paper sheet can be reduced. Consequently, the possibility of the problem of double feeding can be reduced. This is particularly effective for use solely with the thin paper sheets. Of course, the invention is not limited to the embodiments described herein, and various modifications can be made within the scope of the invention as defined in the claims and should be regarded as included in the invention. 

1. A medium feeding device comprising: a placement section where the medium are placed; feeding means that feeds the medium to the downstream region in the feeding direction, the feeding means having a feeding roller that is in contact with the top medium of the stack of media stacked in the placement section, and an arm that is mounted to be movable about a point located above the feeding roller in the stack direction and provided with the feeding roller for rotation at the free end of the arm; and separation means that is provided with an inclined plane so that the leading edge of the medium placed in the placement section abuts the inclined plane and separates the top medium from the subsequent media, wherein a portion of the placement section which opposes the feeding roller is displaceable in directions that allow the portion of the placement section to come into contact with and be separated from the feeding roller, and the feeding roller receives a force from the medium, which causes the arm to move in a direction that causes the feeding roller to move toward the medium, thereby increasing a pressing force of the feeding roller against the medium, such that the portion of the placement section is displaced when the pressing force of the feeding roller against the medium exceeds a predetermined amount of force.
 2. The medium feeding device according to claim 1, wherein the medium feeding device is configured to feed a first medium and a second medium having a hardness higher than that of the first medium, and wherein the portion of the placement section is not displaced by the pressing force when feeding the first medium, and the portion of the placement section is displaced by the pressing force when feeding the second medium.
 3. The medium feeding device according to claim 1, further comprising bias means that biases the portion of the placement section in a direction so as to move the portion of the placement section toward the feeding roller.
 4. The medium feeding device according to claim 3, further comprising a regulation member that regulates the position at the side close to the feeding roller within the range through which the portion of the placement section is displaced.
 5. The medium feeding device according to claim 1, wherein the portion of the placement section is configured to be movable about a position in the downstream area in the feeding direction.
 6. The medium feeding device according to claim 1, wherein the portion of the placement section is configured to be displaced while maintaining its posture.
 7. The medium feeding device according to claim 1, wherein the placement section is configured such that a portion of the placement section at the downstream area in the feeding direction which opposes the feeding roller is displaceable and an area upstream in the feeding direction relative to the downstream area in the feeding direction is not displaceable.
 8. A recording apparatus comprising the medium feeding device according to claim 1 and a recording unit that performs recording on the medium which has been fed by the medium feeding device. 